pw::allocator::BumpAllocator Class Reference

Overview

Allocator that does not automatically delete.

A "bump" or "arena" allocator provides memory by simply incrementing a pointer to a memory region in order to "allocate" memory for requests, and doing nothing on deallocation. All memory is freed only when the allocator itself is destroyed. As a result, this allocator is extremely fast.

Bump allocators are useful when short-lived to allocate objects from small buffers with almost zero overhead. Since memory is not deallocated, a bump allocator with a longer lifespan than any of its allocations will end up holding unusable memory. An example of a good use case might be decoding RPC messages that may require a variable amount of space only for as long as it takes to decode a single message.

On destruction, the destructors for any objects allocated using New or MakeUnique are NOT called. To have these destructors invoked, you can allocate "owned" objects using NewOwned and MakeUniqueOwned. This adds a small amount of overhead to the allocation.

Inheritance diagram for pw::allocator::BumpAllocator:

Public Member Functions
constexpr	BumpAllocator ()
	Constructs a BumpAllocator without initializing it.
	BumpAllocator (ByteSpan region)
	Constructs a BumpAllocator and initializes it.
void	Init (ByteSpan region)
	Sets the memory region to be used by the allocator.
template<typename T , int &... kExplicitGuard, typename... Args>
T *	NewOwned (Args &&... args)
template<typename T , int &... kExplicitGuard, typename... Args>
UniquePtr< T >	MakeUniqueOwned (Args &&... args)
Public Member Functions inherited from pw::Allocator
void *	Allocate (Layout layout)
template<typename T , int &... kExplicitGuard, typename... Args>
std::enable_if_t<!std::is_array_v< T >, T * >	New (Args &&... args)
template<typename T , int &... kExplicitGuard, typename ElementType = std::remove_extent_t<T>, std::enable_if_t< is_bounded_array_v< T >, int > = 0>
ElementType *	New ()
template<typename T , int &... kExplicitGuard, typename ElementType = std::remove_extent_t<T>, std::enable_if_t< is_unbounded_array_v< T >, int > = 0>
ElementType *	New (size_t count)
template<typename T , int &... kExplicitGuard, typename ElementType = std::remove_extent_t<T>, std::enable_if_t< is_unbounded_array_v< T >, int > = 0>
ElementType *	New (size_t count, size_t alignment)
	Constructs an alignment-byte aligned array of count objects.
template<typename T >
T *	NewArray (size_t count)
template<typename T >
T *	NewArray (size_t count, size_t alignment)
template<typename T , int &... kExplicitGuard, std::enable_if_t<!std::is_array_v< T >, int > = 0, typename... Args>
UniquePtr< T >	MakeUnique (Args &&... args)
template<typename T , int &... kExplicitGuard, std::enable_if_t< is_unbounded_array_v< T >, int > = 0>
UniquePtr< T >	MakeUnique (size_t size)
template<typename T , int &... kExplicitGuard, std::enable_if_t< is_unbounded_array_v< T >, int > = 0>
UniquePtr< T >	MakeUnique (size_t size, size_t alignment)
template<typename T , int &... kExplicitGuard, std::enable_if_t< is_bounded_array_v< T >, int > = 0>
UniquePtr< T >	MakeUnique ()
template<typename T >
UniquePtr< T[]>	MakeUniqueArray (size_t size)
template<typename T >
UniquePtr< T[]>	MakeUniqueArray (size_t size, size_t alignment)
template<typename T , int &... kExplicitGuard, std::enable_if_t<!std::is_array_v< T >, int > = 0, typename... Args>
SharedPtr< T >	MakeShared (Args &&... args)
template<typename T , int &... kExplicitGuard, std::enable_if_t< is_unbounded_array_v< T >, int > = 0>
SharedPtr< T >	MakeShared (size_t size)
template<typename T , int &... kExplicitGuard, std::enable_if_t< is_unbounded_array_v< T >, int > = 0>
SharedPtr< T >	MakeShared (size_t size, size_t alignment)
template<typename T , int &... kExplicitGuard, std::enable_if_t< is_bounded_array_v< T >, int > = 0>
SharedPtr< T >	MakeShared ()
bool	Resize (void *ptr, size_t new_size)
bool	Resize (void *ptr, Layout layout, size_t new_size)
void *	Reallocate (void *ptr, Layout new_layout)
void *	Reallocate (void *ptr, Layout old_layout, size_t new_size)
size_t	GetAllocated () const
Public Member Functions inherited from pw::Deallocator
constexpr const Capabilities &	capabilities () const
bool	HasCapability (Capability capability) const
	Returns whether a given capability is enabled for this object.
void	Deallocate (void *ptr)
void	Deallocate (void *ptr, Layout layout)
template<typename ElementType >
void	DeleteArray (ElementType *ptr, size_t count)
StatusWithSize	GetCapacity () const
bool	IsEqual (const Deallocator &other) const
template<typename T , int &... kExplicitGuard, std::enable_if_t<!std::is_array_v< T >, int > = 0>
void	Delete (T *ptr)
template<typename T , int &... kExplicitGuard, typename ElementType = std::remove_extent_t<T>, std::enable_if_t< is_bounded_array_v< T >, int > = 0>
void	Delete (ElementType *ptr)
template<typename T , int &... kExplicitGuard, typename ElementType = std::remove_extent_t<T>, std::enable_if_t< is_unbounded_array_v< T >, int > = 0>
void	Delete (ElementType *ptr, size_t count)

Static Public Attributes
static constexpr Capabilities	kCapabilities = kSkipsDestroy

Private Member Functions
void *	DoAllocate (Layout layout) override
void	DoDeallocate (void *) override
size_t	DoGetAllocated () const override

Additional Inherited Members
Public Types inherited from pw::Deallocator
using	Capabilities = allocator::Capabilities
using	Capability = allocator::Capability
using	Layout = allocator::Layout
Protected Member Functions inherited from pw::Allocator
constexpr	Allocator ()=default
	TODO(b/326509341): Remove when downstream consumers migrate.
constexpr	Allocator (const Capabilities &capabilities)
Protected Member Functions inherited from pw::Deallocator
constexpr	Deallocator ()=default
	TODO(b/326509341): Remove when downstream consumers migrate.
constexpr	Deallocator (const Capabilities &capabilities)
template<typename T , int &... kExplicitGuard, typename ElementType = std::remove_extent_t<T>, std::enable_if_t< is_unbounded_array_v< T >, int > = 0>
UniquePtr< T >	WrapUnique (ElementType *ptr, size_t size)
Static Protected Attributes inherited from pw::Deallocator
template<typename T >
static constexpr bool	is_bounded_array_v
template<typename T >
static constexpr bool	is_unbounded_array_v

Member Function Documentation

DoAllocate()

void * pw::allocator::BumpAllocator::DoAllocate ( Layout  layout )

overrideprivatevirtual

Allocates a block of memory with the specified size and alignment.

Returns nullptr if the allocation cannot be made, or the layout has a size of 0.

Parameters

[in]

layout

Describes the memory to be allocated.

Implements pw::Allocator.

DoDeallocate()

void pw::allocator::BumpAllocator::DoDeallocate ( void *  )

overrideprivate

Releases a previously-allocated block of memory.

The given pointer must have been previously provided by this memory resource; otherwise the behavior is undefined.

Parameters

[in]

ptr

Pointer to previously-allocated memory.

DoGetAllocated()

size_t pw::allocator::BumpAllocator::DoGetAllocated ( ) const

inlineoverrideprivatevirtual

Returns the total bytes that have been allocated by this allocator, or size_t(-1) if this allocator does not track its total allocated bytes.

Reimplemented from pw::Allocator.

MakeUniqueOwned()

template<typename T , int &... kExplicitGuard, typename... Args>

UniquePtr< T > pw::allocator::BumpAllocator::MakeUniqueOwned ( Args &&...  args )

inline

Constructs and object of type T from the given args, and wraps it in a UniquePtr

Owned objects will have their destructors invoked when the allocator goes out of scope.

The returned value may contain null if allocating memory for the object fails. Callers must check for null before using the UniquePtr.

Parameters

[in]

args...

Arguments passed to the object constructor.

NewOwned()

template<typename T , int &... kExplicitGuard, typename... Args>

T * pw::allocator::BumpAllocator::NewOwned ( Args &&...  args )

inline

Constructs an "owned" object of type T from the given args

Owned objects will have their destructors invoked when the allocator goes out of scope.

The return value is nullable, as allocating memory for the object may fail. Callers must check for this error before using the resulting pointer.

Parameters

[in]

args...

Arguments passed to the object constructor.

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The documentation for this class was generated from the following file:

• pw_allocator/public/pw_allocator/bump_allocator.h